1. Field of the Invention
This invention relates to a refractory plate for a slide gate (hereinafter referred to as "slide-gate plate"), and particularly to a refractory plate which is formed of a base plate and a separate plate disposed at the center portion of the base plate in combination, and which has an inactive-gas supply groove on a slide surface thereof.
2. Description of Related Art
A slide gate device has been conventionally widely used with being connected to a ladle or a tundish which is used in a molding process for iron and steel. As shown in FIG. 1, the slide gate device includes an upper nozzle 2 mounted through a nozzle support brick 3 at the lower portion of a ladle 1, a fixed plate 4, a slide plate 5 and a lower nozzle 6 which are mounted at the lower side of the upper nozzle 2, and a nozzle hole 7 which is formed at the center of the upper nozzle 2 and the lower nozzle 6 so as to vertically penetrate through the upper and lower nozzles 2 and 6. The slide plate 5 is slidably moved by manipulating a drive member 8 which is linked to a hydraulic driving source (not shown), and through the sliding motion of the slide plate 5, the opening and closing operation of the nozzle hole 7 is controlled to carry out various control operations such as an operation of adjusting flow-amount of molten metal (not shown), an operation of ceasing flow-out of the molten metal, etc.
In the slide gate device as described above, the inside of the nozzle hole 7 is kept in a negative-pressure state when molten metal falls into or flows out of the nozzle hole 7, and thus outside air is sucked into the nozzle hole 7 through a gap between the slide surfaces of the fixed plate 4 and the slide plate 5. Therefore, this device has have a problem that the ingot steel is subjected to oxidation or nitrogen pickup. In order to solve this problem, conventionally, a slender groove is formed around the nozzle hole on the slide surface of the fixed plate or the slide plate of the device, and inert gas is supplied to the slender groove to prevent the outside air from being sucked into the slide surface between the fixed plate and the slide plate.
In a case where refractory material is used as raw material for the plate having the groove for the slide gate as described above, the refractory material is required to be fine and have high strength, and also the groove is required to be formed minutely and with high accuracy. Therefore, the slender groove is not necessarily easily formed.
That is, in order to integrally form a groove in a molding process, a mold comprising upper and lower molds one of which is formed with a projection corresponding to the groove is required. such a mold is expensive in cost, and its yield is remarkably lowered because an edge portion of the groove is liable to be chipped off in the molding process.
In place of the above method, the following method may be adopted to form a groove. That is, a combustible (plastic, paraffin or the like) having a shape corresponding to the profile of the groove is beforehand prepared. The combustion is molded at a predetermined position together with mixture, and then combusted in a sintering process to form a groove. However, this method can hardly provide a product with excellent accuracy.
Further, a groove may be formed in a working process after the sintering process. However, the working cost is high, and it is difficult to conduct the working on fine refractory material such as high alumina refractory, alumina-carbon refractory, etc. Therefore, restriction is imposed on selection of refractory material.
Still further, when high-temperature fluid such as molten metal or the like flows out, a large temperature difference occurs between the peripheral portion of the flow-out nozzle hole of the gate plate and the outer portion away from the nozzle hole, and thus some kinds of materials constituting these portions are frequently damaged by thermal shock. Therefore, refractory material which has high resistance against thermal shock, but has relatively-low fineness has been used for the gate plate device, and such material has a problem in corrosion resistance.